1. Field of the Invention
The present invention relates to an electromagnetic driving type lens driving device used in a camera assembly for a mobile telephone.
2. Description of Related Art
FIG. 7 is an exploded view of an existing voice coil motor type lens driving device 20. Moreover, the direction the same as the direction of the optical axis O of the lens 25 is taken as Z axis direction, and two directions which are orthogonal to the Z axis and are mutually orthogonal are taken as X axis direction and Y axis direction. Moreover, the side of an object to be shot is taken as the front side (front of the Z axis, +Z side) of the direction of the optical axis O (Z axis direction). Moreover, a direction of an axis formed by rotating the X axis around the Z axis by 45 degrees is taken as P axis direction, and a direction of an axis formed by rotating the Y axis around the Z axis by 45 degrees is taken as Q axis direction.
The lens driving device 20 includes an annular magnet yoke 22, four permanent magnets 23, a lens support 24, a lens 25, a coil 26, a front side spring component 21A, a back side spring component 21B and a box body 27.
The magnet yoke 22 includes an outer circumference wall 22a formed to be a quadrangular barrel shape when being observed in the Z axis direction, an inner circumference wall 22b formed to be a cylindrical shape, and a tubular top surface 22c for mutually connecting the +Z side of the outer circumference wall 22a with the +Z side of the inner circumference wall 22b. The permanent magnets 23 are mounted on the inner sides of four corners of the outer circumference wall 22a of the magnet yoke 22.
The lens support 24 is formed to be a cylindrical shape, and the lens 25 is retained on the inner circumference side of the lens support 24. And the lens support is supported by the front side spring component 21A and the back side spring component 21B on the inner circumference side of the inner circumference wall 22b of the magnet yoke 22, so that the lens support 24 can move along the Z axis direction. The coil 26 is positioned between the inner circumference wall 22b of the magnet yoke 22 and the permanent magnets 23 with intervals, and is mounted on the outer circumference side of the lens support 24.
As shown in FIG. 8, the front side spring component 21A is integrally formed to be annular. The front side spring component 21A includes: an inner side retaining part 21a which is arranged on the inner circumference side and formed to be circular ring-shaped, an outer side retaining part 21b which is arranged on the outer circumference side and formed to be square frame-shaped, and two wrist parts 21c which are zigzagged along the circumferential direction. One ends of the wrist parts are connected with the inner side retaining part 21a, and the other ends of the wrist parts are connected with the outer side retaining part 21b. These wrist parts 21c are respectively arranged at the diagonal position of the outer side retaining parts 21b in the P axis direction.
The back side spring component 21B is divided into two parts along the Y axis direction. The back side spring component 21B includes: two inner side retaining parts 21a which are arranged on the inner circumference side and formed to be circular arc-shaped, two outer side retaining parts 21b which are arranged on the outer circumference side and formed to be -shaped, and two wrist parts 21c which are zigzagged along the circumferential direction. One ends of the wrist parts are connected with the inner side retaining part 21a, and the other ends of the wrist parts are connected with the outer side retaining part 21b. These wrist parts 21c are respectively arranged at the diagonal position of the outer side retaining parts 21b in the Q axis direction.
The inner side retaining parts 21a of the front side spring component 21A and the back side spring component 21B are connected with the front side and the back side of the lens support 24 in the Z axis direction. The outer side retaining parts 21b are respectively connected with the front side and the back side of the magnet yoke 22 in the Z axis direction arranged on the side of the box body. Moreover, four supporting columns 27a are arranged at four corners of the box body 27, and the four corners of the magnet yoke 22 are inlaid in the inner side of the supporting columns 27a, so that the lens driving device 20 (referring to FIG. 7) is formed.
When the coil 26 is electrified so as to enable the lens driving device 20 to realize focusing, pushing force towards the front of the Z axis direction is applied to the coil 26, so that the lens support 24 moves forward in the Z axis direction to the position that the pushing force and restoring force generated by the front side spring component 21A and the back side spring component 21B achieve a balance. At this moment, when the wrist parts 21c of the front side spring component 21A and the wrist parts 21c of the back side spring component 21B are connected with the lens support 24 at a same angle in an undistorted/untwisted manner (for example, the wrist parts 21c of the front side spring component 21A and the wrist parts 21c of the back side spring component 21B are disposed at the diagonal position in the P axis direction all together), the lens support 24 moves along the Z axis direction for focusing, and the lens support 24 is likely to rotate or incline around the P axis.
Therefore, the wrist parts 21c of the front side spring component 21A are arranged at the diagonal position in the P axis direction, and the wrist parts 21c of the back side spring component 21B are arranged at the diagonal position in the Q axis direction formed by rotating the Y axis by 90 degrees when being observed in the direction of the optical axis O. Therefore, when the lens support 24 moves towards the Z axis direction along with the focusing action, the lens support 24 can be prevented from rotating or inclining around a specific axis perpendicular to the Z axis as mentioned above (for example referring to patent documentation 1: JP Patent No. 2008-26619).
Under the condition that the image is shot by the camera, the camera may face to different directions sometimes, or the camera rotates around the optical axis O of the lens 25. Namely, the camera takes photos at a posture that the optical axis O of the lens 25 faces to the vertical direction, or at a posture that the optical axis O of the lens 25 faces to the horizontal direction, or at a posture that the lens 25 rotates around the optical axis O towards the horizontal direction.
As shown in FIG. 9A, FIG. 9B and FIG. 9C, for example, under the condition that the camera shoots by enabling the lens driving device 20 to rotate around the optical axis O at the manner that the optical axis O of the lens 25 faces to the horizontal direction and the P axis direction faces to the vertical direction, load W generated by the lens 25, the lens support 24 and the coil 26 is applied to the wrist parts 21c of the front side spring component 21A and the wrist parts 21c of the back side spring component 21B towards the P axis direction.
As mentioned above, the wrist parts 21c of the front side spring component 21A are arranged at the diagonal position of the lens driving device 20 in the P axis direction, and the wrist parts of the back side spring component 21B are arranged at the diagonal position of the lens driving device 20 in the Q axis direction. On the other hand, the spring strength of the wrist parts 21c of the front side spring component 21A is different based on the load W suffered in different directions, and the spring strength generated in the P axis direction is lower, the spring strength generated in the Q axis direction is higher. Moreover, the spring strength of the wrist parts 21c of the back side spring component 21B is bias in different directions, and the strength in the P axis direction is higher, the strength in the Q axis direction is lower.
Therefore, as shown in FIG. 9D, even if the load W is equivalently applied to the wrist parts 21c of the front side spring component 21A and the wrist parts 21c of the back side spring component 21B respectively, and the displacement in the front of the lens support 24 is greater than the displacement at the back of the lens support 24 towards the P axis direction, so that the lens support 24 inclines around the Q axis direction. Moreover, under the condition that the optical axis O of the lens 25 is disposed in the horizontal direction and then the Q axis direction faces to the vertical direction, oppositely, the displacement at the back of the lens support 24 is greater than the displacement in the front of the lens support 24 toward the Q axis direction, so that the lens support 24 inclines around the P axis direction.
As mentioned above, under the condition that the optical axis O of the lens 25 in the existing lens driving device 20 faces to the horizontal direction, the lens 25 is likely to incline, so that the image imaged on the image sensor is likely to appear distortion and deformation.